Calculating Vrms from a given function

Discussion in 'Homework Help' started by blalaw, Feb 11, 2014.

  1. blalaw

    Thread Starter New Member

    Oct 28, 2013
    I need to calculate the effective RMS values given
    a) g(t) = 2 + 3cos(100t) + 4cos(100t - 120)
    b) h(t) = 2 + 3cos(100t) + 4cos(101t - 120)

    I am pretty sure the first one is straight forward since 2 is a constant voltage then the value will just be two the second part would be 3/sqrt(2) and the last part would be 4/sqrt(2) in phase -120 degrees and just add them up if that is correct I believe.

    The second part I am kind of lost because I am not sure what to do with the 101t since it is not the same as the 100t.
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    What result do you get for the first part after you add them up?
  3. WBahn


    Mar 31, 2012
    Ask yourself if the method you are trying to use makes sense in the limiting cases.

    For instance, what if you have

    v(t) = 3V cos(ωt) + 4V cos(ωt + 180°)

    Or what if you have

    v(t) = 3V cos(ωt) + 4V cos(ωt + 0°)